Behavioral economics has described many ways in which choice deviates from normative (i.e., optimal) behavior. For example, a pervasive feature of human decision-making is probability distortion: humans tend to overweight small probabilities and underweight large probabilities. When individuals decide to purchase insurance or play the lottery, these decisions are influenced by how likely they perceive low probability outcomes to be. Another ubiquitous decision bias is called the Hot-Hand FallacyS in which people mistakenly perceive random successes as winning streaks, believing that they have a hot hand. These near universal phenomena may reflect fundamental aspects of the neural substrates of decision-making. Decision-making is disrupted in psychiatric disorders including schizophrenia and bipolar disorder9-14. A circuit-level understanding of how the brain represents probabilisties during decision-making has great consequences for human health. I have recently used high-throughput behavioral training to develop behavioral paradigms for studying probability distortion in rats, enabling application of powerful tools to monitor and manipulate neural circuits. In this task, rats chose between probabilistic and guaranteed rewards. I have performed tetrode recordings from two brain regions during this behavior, posterior parietal cortex (PPC) and orbitofrontal cortex. I performed optogenetic perturbations of these regions, and while these did not perturb rats' probability distortion, they produced an intriguing effect. Rats exhibited a Hot-Hand Bias, in which they were more likely to gamble following risky choices that were rewarded. Optogenetic inhibition of OFC eliminated the hot-hand bias in 13 rats; inhibition of PPC had no effect on the hot-hand bias. Therefore, thus far, we have identified a brain region, the OFC, as causal to a ubiquitous decision bias that demonstrably affects human behavior in finance, gambling, and professional sports. I am in the process of preparing and submitting two manuscripts about this work so far. I have been trained in all of the techniques required to complete the R00 phase of the award. In the R00 phase, I will perform optogenetic and pharmacological perturbation experiments to delineate the functional causal circuits underlying probability distortion. I will also use projection-specific optogenetic and recording methods to explore whether specific subcircuits of neurons in OFC are preferentially responsible for mediating the hot-hand bias. Together, these experiments will establish the rat as a cost-effective, tractable mammalian model for studying the neural basis of decision biases and will produce well-informed working models of the circuits and mechanisms by which animals compute, represent, and distort probability estimates. I have secured a tenure-track position as an Assistant Professor in the Center for Neural Science at New York University. In 00 phase, I will use the skills I have acquired during the K99 phase to complete the proposed aims and build a laboratory focused on the study